Behind either condyle of the lateral parts of occipital bone is a depression, the condyloid fossa (or condylar fossa), which receives the posterior margin of the superior facet of the atlas when the head is bent backward; the floor of this fossa is sometimes perforated by the condyloid canal, through which an emissary vein passes from the transverse sinus.
Human skull seen from below. Position of condyloid fossa shown in red.
X-ray of cervical spine (neck) in flexion and extension (bending backwards)
This article incorporates text in the public domain from the 20th edition of Gray's Anatomy (1918)